A power supply system including a secondary battery is used in various equipment and systems, a typical example of which is a hybrid vehicle. The secondary battery has a temperature range in which the charging efficiency thereof is sharply reduced when the temperature of the secondary battery itself rises by heat generated as the secondary battery is charged and discharged. Therefore, such a power supply system requires a cooling system for a secondary battery.
For this type of a secondary battery cooling system, there has conventionally been proposed a configuration that controls on/off of a cooling fan in accordance with the temperature of the secondary battery to cool the secondary battery. The cooling fan is operated to prevent the temperature rise so that the temperature of the secondary battery can be kept within an appropriate temperature range.
However, an anomaly may occur in the secondary battery cooling system. For example, there may be a case where the cooling fan is made inoperable because of wire breaking and others, or a case where the cooling fan is made uncontrollable because of an anomaly of the control system thereof and others. Alternatively, a cooling air path may be clogged with dust so that the circulation of air serving as a cooling medium is blocked, although neither mechanical nor electrical anomaly occurs in the cooling system. Such an anomaly of the cooling fan directly affects the cooling state of the secondary battery, and hinders the secondary battery in use from delivering a desired performance. In view of these points, various configurations that detect a failure of the secondary battery cooling fan have been proposed.
For a power supply device provided with a cooling fan for cooling a secondary battery, for example, there has been proposed a configuration that calculates an assumed amount of temperature change of the battery, from input and output power and a temperature difference between the temperatures of the battery and a cooling medium, and based on the result of comparison between the assumed amount of temperature change and an actual amount of temperature change, senses a failure of the battery cooling fan (e.g. in Japanese Patent Laying-Open No. 2001-86601).
Alternatively, there has been proposed, for example, a configuration that monitors the temperature of cooling air after a driving signal is output to a battery cooling fan, and detects a failure of the cooling fan if an amount of temperature drop of the cooling air is small (e.g. in Japanese Patent Laying-Open No. 2001-210389), or a configuration that senses a failure of a cooling system if a deviation of an actual battery temperature from an expected battery temperature, which is calculated from charge and discharge current and a cooling state, is large (e.g. in Japanese Patent Laying-Open No. 2001-313092).
However, if another power supply (voltage generator), which can be a heat generation source, is disposed in proximity to the secondary battery, a configuration for efficiently cooling both of them is required. For a power supply device in which a DC/DC converter that supplies a power supply voltage to other equipment and others is disposed in proximity to the secondary battery, for example, such a configuration is required.
Such a power supply device adopts a configuration in which individual cooling fans are provided to correspond to the secondary battery and the DC/DC converter, respectively, and arranged in parallel, to ensure sufficient cooling capacity for both of the secondary battery and the DC/DC converter.
In such a configuration with parallel arrangement, the cooling fans may be in proximity to each other, and flows of air serving as a cooling medium (coolant) may affect each other. It is therefore necessary to control both of the cooling fans in a coordinated manner. In a configuration in which a revolution speed sensor and others are disposed to detect a failure of the cooling fans, the number of failure detection sensors to be disposed increases as the number of the cooling fans to be disposed increases, which result in cost increase. If a malfunction of the failure detection sensors themselves is considered, in particular, reliability of the failure detection is decreased as the number of the cooling fans to be disposed increases.
Accordingly, in a power supply device provided with a plurality of cooling fans, it is desirable to detect a failure of the cooling fans without providing a sensor that detects an operating state of the cooling fans.